# E-Mail Adresses

Guy Carpenter (Guy.Carpenter@bushnet.qld.edu.au)
Sun, 21 Jan 1996 18:24:07 PST

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    At 06:08 PM 21/01/96 PST, Matt Pauker wrote:

    >You could just finger the user - Connect to port 79 of the domain (In this
    >case castle.net), and just send the username (david).  If you get anything
    >other than:
    >
    >finger: <username>: no such user
    >
    >Then the email is valid.

    I'm afraid that's not very general because:
    * lots of people use aliases (like First.Last@host) instead of usernames,
    * lots of email addresses have no hostname (like First.Last@domain)
      and domain may not resolve to an IP address.

    If you were going to try this it would probably be better
    to use the SMTP VRFY command by doing something like
    this:
    *  look up the MX records associated with the domain part.
        if you don't find it then try resolving the domain itself.
    *  Open a connection to port 25 on host you have chosen.
    *  Send the command VRFY <emailaddress>
    *  check the numeric response code - 500's are good, 200's are bad

    But be warned - some SMTP servers will say anything is fine.

    I've used this technique for verifying large databases of email address
    and it works pretty well - probably better than 90% can be
    tested this way.

    -Guy.
    ----------------------------------------------------------------------
    Guy Carpenter - Clearwater Technical Services
    Tel: (070) 953309                  Fax: (070) 953007
    Email: Guy.Carpenter@bushnet.qld.edu.au
    ----------------------------------------------------------------------